Historically the earliest wheel was believed to be little more than a circular solid piece of wood with a hole in the center. The centered hole was the hub for the wheel to rotate around. This design worked as a means to carry several objects at a time, but it was very heavy, requiring large animals to effectively move the objects at a tedious pace.
The first major improvement to the wheel was the use of spokes. This was such a grand improvement that it in turn brought forth the first major vehicle, the chariot. Spokes were a basic support structure that met the minimum requirements to withstand the multiple forces that a wheel sustains. A pair of spokes used the minimum three points of contact to constitute a rigid frame. This rigid frame formed the shape of a triangle that could be traced by going from the hub to two spoke mounting points on the wheel rim and back again. Several of those triangles would extend from the hub in all directions to support the whole circumference of the wheel rim and they created a visibly repetitive pattern. Although the number and size of the spokes used for wheels have changed over the years, they still serve the same purpose.
The next improvement was the tire. This hoop of metal or rubber was used to protect the wheel rim from harsh road conditions, allowing for a longer wheel life.
Then the pneumatic tire was introduced to help soften the damages caused by the road. The pneumatic tire, being little more than a rubber balloon, was able to absorb road vibration, lighten tire weight, and give the wheel a larger contact surface. Unfortunately, like a balloon, the pneumatic tire could be popped. Nylon and steel belts were eventually added to the tire to strengthen the rubber and give it a more consistent shape. However, this did not eliminate air leaks or any of the other flaws associated with the pneumatic tire.
More recently there have been attempts to reduce the air loss of a pneumatic tire by filling it with various materials, but these attempts have also fallen victim to the various flaws associated with either the heavy unforgiving solid tires or the delicate pneumatic tires of the past.